Waste disposal is rapidly becoming one of our society's most critical problems. An environmentalist recently commented that the United States waste stream could be cut by 25% if people composted their food and yard wastes. D. Stipp, Wall Street Journal, Feb. 21, 1991, page B1. In addition to the significant advantages of waste recycling, composting provides gardens with an exceptionally rich nutritional source without substantial expense.
Composting is a biochemical process in which organic substances are reduced from large volumes of rapidly decomposable materials to smaller volumes of materials which continue to decompose slowly. In this process, the ratio of carbon to other elements is brought into balance, thus avoiding temporary immobilization of nutrients. One of the many benefits of adding compost to the soil is that the nutrients in it are slowly released to the soil and are then available for use by plants. Decomposition will take place in soil if undercomposed organic materials are added to it, but in the breakdown process nutrients will be tied up and unavailable for plants to use. This may result in nutrient deficiencies and poor growth, especially if large amounts of undercomposed matter is added.
Prior composting methods have involved simply piling organic materials over the earth and letting them stand for long periods of time until the materials were sufficiently decomposed to be ready for use. This method does not require special tools, and minimal time and effort is required to initiate and oversee the process. However, there are disadvantages: ground space is utilized for extended periods; some nutrients will leach away due to exposure to rainfall; and disease producing organisms, weed seeds and insects are not controlled.
Over the years, as the composting process has been studied and become better understood, the major objectives have been elucidated and given rise to various designs for compost containers ("composters").
Heat retention is an important composting requirement, heat being generated by the respiration of microorganisms as they break down the organic materials. Heat retention is enhanced when the compost is held within a container. Composter lids help to further the heat retention objective. However, many existing composter containers have too many vents or holes allowing heat to escape and negating any substantial significant insulation effects resulting from the container. Prior compost manufacturers have tried to accomplish heat retention by lining the composter with an insulating material. However, the insulator must be non-biodegradable and must allow some aeration from the outside. Even if such materials are available, they add manufacturing complications and increase material costs.
Another important requirement for effective composting is frequent mixing. Because of heat transfer limitations, the center of the compost pile can become extremely hot. If it gets too hot, the microorganisms responsible for the decomposition process will die, the pile will cool, and the whole process will have to start over. Frequent turning and mixing of the pile helps to prevent the overheating problem. Additionally, since the temperature in an unturned compost will be uneven, i.e. hotter toward the middle of the pile, composting rates will vary throughout the pile. Due to heat loss around the margins, only the central portion of the pile is at the optimum temperature. The pile should be turned so that material which is on the outside is moved to the center. In this way, all the material will reach optimum temperatures at various times.
Compost mixing helps to achieve the objective of aeration, which is necessary for effective composting. The objective of aerating the compost competes with the objective of heat containment. If too much non-porous insulation is put around the compost pile to retain heat, it will prevent aeration and suffocate the composting process. On the other hand, if too much external air access is provided, the retained heat will readily escape. Most prior composters suffer from one of these two problems. Nevertheless, composters require some mixing in order to adequately aerate the inner portions of the compost.
Many prior composters are not designed to allow efficient mixing. One attempt to solve this problem involves providing a door or slat on the side of the compost container. However, this design only facilitates mixing of the compost which is adjacent to the opening. Another approach has been to put the compost in a bin which is equipped with a mechanical apparatus for rolling or rotating the bin. While this approach can yield good composting results, it requires extra mechanical parts which complicates production and maintenance.
While general composting goals have been understood in the art, no single compost design has been available prior to the present invention, which simultaneously addresses and adequately solves each of the design considerations of heat containment, mixing flexibility and aeration.